If I had known where he lived, I would have been able to go to his house.
If I knew where he lived, I would have gone to his house.
「彼がどこに住んでいるか知っていたら」は
If I had known where he lived,
If I knew where he lived,
のように表現できます。
例:
If I had known where he lived, I would have been able to go to his house, but I don't know where he lives, so I can't go there.
「もし彼がどこに住んでいるか知っていたら、彼の家にいくことができたのに、知らないから行くことができない」
ご参考まで!